Bring a large pot of salted water to a boil, then add the chopped bok choy stems. Cook until just tender, about 5 minutes, and then add the leaves for another 30 seconds. When finished, drain in a colander and rinse under cold water. When they are cool enough to handle, squeeze out any excess water with your hands.

Next, cook the shallot with a tablespoon of butter in a pan over medium heat, stirring until softened, about 2 minutes. Add the bok choy and cook, stirring until it is completely coated with butter, for another couple minutes. Spread the mixture out in the baking dish.

Now you can start making the roux. Melt 2 tablespoons of butter in a small saucepan over medium-low heat, then add the flour and stir constantly for about 2 minutes.

Add the milk in a slow stream, whisking constantly. Bring to a boil (still whisking), then reduce heat and simmer for 5 minutes. Add the nutmeg, salt & pepper, then stir in the Gruyere and half the Parmesan and pour evenly over the bok choy.

In a small bowl, toss 1/4 cup of breadcrumbs with the rest of the Parmesan and work in 2 tablespoons of butter with your fingers, until the mixture resembles a coarse meal. Season with salt & pepper and sprinkle the mixture over the gratin. Bake until bubbly and golden brown, about 20 minutes, then take it out and increase the oven to 550° F.

Meanwhile, saute the mushrooms in a pan with a bit of olive oil and salt, until they are nice and soft.

When the oven is hot, you can prepare your dough using the instructions here. Once you’ve baked it for a minute, take it out and brush it lightly with olive oil.

Spoon the gratin onto the pizza so that it coats it evenly (you might not use the whole thing, don’t overdo it). Then add an even layer of mushrooms and fava beans. Sprinkle some extra breadcrumbs on top to add a layer of crunch, then pop it in the oven. Bake until the crust and breadcrumbs are golden brown, then take it out and enjoy!

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